chore(deps): update dependency postcss to v8.4.18

Author: renovate[bot]

package-lock.json

@@ -69,7 +69,7 @@
     "minimist": "1.2.7",
     "mkdirp": "1.0.4",
     "mocha": "10.0.0",
-    "postcss": "8.4.17",
+    "postcss": "8.4.18",
     "postcss-map": "0.11.0",
     "power-assert": "1.6.1",
     "prettier": "2.7.1",